It is desirable that a hydraulically-assisted engine valve actuator provide for flexible engine valve operation under a wide band of engine operating conditions. The hydraulically-assisted engine valve actuator should provide for variable valve timing of closing and opening and variable lift as desired in order to achieve the greatest engine efficiencies. Presently, hydraulic fluid is supplied to hydraulically actuated valves through tubes commonly called rails. Valve motion profiles in current hydraulic actuation designs depend on a pre-established constant value of oil pressure at the supply rails because rail pressures cannot be adjusted fast enough to modulate valve profiles. The constant rail pressure values result in constant valve profiles regardless of engine rpm.
Present hydraulic actuation schemes add complexity to the engine design. Some hydraulic actuation designs rely on additional hydraulic supply rails at constant pressure levels. Further, hydraulic actuation that relies on on/off solenoid (spool or poppet) valve operations require engine valve position sensors for reliable timing of the solenoids and for safe operation. The plurality of sensors required, further adds to the engine complexity.
A hydraulically-assisted engine valve actuator should provide for uniform valve actuation over a wide range of hydraulic fluid temperatures. Present hydraulic actuation schemes typically rely on mechanical damping mechanisms for seating in order to prevent the valve from seating too rapidly. Such mechanisms are typically very dependent on oil temperature, leading to nonuniform valve actuation characteristics.